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天津工程师范学院学生毕业设计（论文）中期报告系别电子系班级应电041学生姓名陈春秀指导教师葛颖 课题名称：红外遥控发射接收电路设计简述开题以来所做的具体工作、取得的进展及下一步主要工作：1、 开题以来所做的具体工作和取得的进展或成果在图书馆和网上收集相关资料，学习了单片机理论，在此基础上，对单片机有了一个整体的认识，基本完成了前面理论部分的学习。经过查阅大量的相关资料，现在已经对红外遥控的原理有了一个清晰深入的了解，对单片机控制系统及其原理进行了详细分析，并对单片机的接口电路都进行了详细的了解。现在正在完成相关电路的制作及相关程序的编写，并解决在此过程中所遇到的问题，收集制作过程中的相关资料，为毕业论文的撰写准备资料。 2、存在的具体问题在制作过程当中要不断的对程序进行修改，由于对单片机编程掌握不是很熟练，在实际调试过程中有一定的困难。关于红外遥控发射机接收电路设计设计资料掌握不全面，因此在实际的电路制作、调试以及相关程序的编写中存在一定的困难。3、下一步的主要研究任务，具体设想与安排继续电路制作以及相关程序调试，得出结果。制作出实用的由单片机控制的红外遥控发射机接收电路，即可完成遥控发射通过扫描按键，每按下一个键，即产生具有不同的编码数字脉冲，这种代码指令信号调制在40KHZ的截波上，激励红外光二级管产生具有脉冲串的红外波，通过空间的传送到受控机的遥控接收器。在接收过程中，红外波信号通过接收头转换为40KHZ的脉冲信号，送到解码与接口电路，从而完成相应的遥控功能。根据掌握的毕业设计的相关资料以及在调试过程中所遇问题的解决的相关资料，着手撰写论文。 学生签字： 2007年5月18日指导教师的建议与要求： 指导教师签字： 2007年5月18日注：本表格同毕业设计（论文）一同装订成册，由所在单位归档保存。天津工程师范学院毕业设计（论文）任务书 2006年 10月 15日题 目（包括副标题）红外遥控电路设计教师姓名葛颖系 别电子工程职 称讲师学生姓名陈春秀班 级应电041学 号21课题成果形式论文 设计说明书 实物 软件 其它1毕业设计（论文）课题任务的内容和要求（如原始数据、技术要求、工作要求等）：1、毕业设计主要内容 1红外遥控电路设计；22006 年11月9日完成开题报告；3画出标准电路原理图（电子板），给出测试点电压或电流；42007年5月10日完成中期报告；5制作实际电路（手工焊接），描述硬件电路特性；6本专业英语译文3000字符以上（内容自选、应与毕业设计题目密切相关）；7撰写毕业设计论文（10000字以上）；82007年6月1日提交毕业论文初稿；9根据学院的具体要求，完成毕业答辩相关事宜。2毕业设计（论文）工作进度计划：周 次工作内容2006年10月15 日2006年11月9 日第一周第二周第三周第四周第五周第六周第七周第八周下达毕业设计任务书开题报告查阅相关资料，确定设计方案；、设计电路设计电路方案确定提交中期报告、购买电子元器件焊接电路、软件编程、调试电路修改毕业论文、毕业论文预答辩撰写毕业论文、提交毕业论文初稿准备答辩，对设计内容进行总结，弄懂各部分的原理及系统的工作过程，写出毕业答辩的发言稿，做到心中有数，应对毕业答辩。 教研室（学科组）主任签字： 毕业设计（论文）开题报告 题目：红外遥控电路设计 系 别： 电子工程系 班 级： 应电041班 学生姓名： 陈春秀 指导教师： 葛颖 2006年11月9日开题报告填写要求1开题报告作为毕业设计答辩委员会对学生答辩资格审查的依据材料之一，应在指导教师指导下，由学生在毕业设计工作前期完成，经指导教师签署意见、专家组及系主任审查后生效；2开题报告必须用黑墨水笔工整书写或按教务处统一设计的电子文档标准格式（可从教务处网页上下载）打印，禁止打印在其它纸上后剪贴；3毕业设计的开题报告应包括以下内容：（1）主要技术指标；（2）工作思路；（3）课题的准备情况及进度计划；（4）参考文献。4开题报告的撰写应符合科技文献规范，且不少于2000字；参考文献应不少于15篇，包括科技期刊、教科书、专著、外文等。 5开题报告正文字体采用宋体小四号，1.5倍行距。附页为A4纸型，左边距3cm，右边距2cm，上下边距为2.5cm，字体采用宋体小四号，1.5倍行距。毕业设计（论文）开题报告课题题目红外遥控电路设计课题类型 工程设计课题来源自拟成果形式实作同组同学无开题报告内容（可另附页） 毕业设计开题报告：（后接附页）指导教师意见（课题难度是否适中、工作量是否饱满、进度安排是否合理、工作条件是否具备等）指导教师签名： 月 日 专家组及系里意见（选题是否适宜、各项内容是否达到毕业设计（论文）大纲要求、整改意见等）专家组成员签字： 教学主任（签章）： 月 日附件：开题报告红外遥控电路设计（一）研究的现状和发展趋势随着当今世界经济的快速发展和信息化时代的来临，各种各样的电子产品陆续出现在我们的生活中。而我所要设计的红外遥控发射机就属其中。红外遥控广泛应用于家庭、银行、证券、邮电、宾馆、医院、学校、企业、商店等相关行业的大厅，以及单位会议室、门卫等场所。在多媒体教学系统的使用、开发和研制中，经常遇到同时使用多种设备，如：数字投影机、DVD、VCD、录像机、电视机等，由于各种设备都自带遥控器，而且不同的设备所遵循的红外传输规约也不尽相同，操纵这些设备得使用多种遥控器，给使用者带来了诸多不便。我想通过这次毕业设计，实做出一个用途这么广泛的红外遥控电路。希望在此过程中，通过实践系统学习51单片机编程，深入了解红外遥控电路的制作和设计过程等相关知识。（二）主要任务以及主要技术指标红外遥控是目前使用最广的一种遥控手段。红外线遥控装置具有体积小、功耗低、功能强、成本低等特点。在家庭生活中，录音机、音响设备、空调采电都采用了红外遥控系统。利用红外传输控制指令，基于和单片机的编程设计，借助单片机强大灵活的控制功能发出脉冲编码，组成一个遥控系统。遥控范围：46米显示可控制的通道：接收灵敏可靠，抗干扰能力强控制用电器（灯具）电流最高为2A红外遥控系统由发射和接收两大部分组成，系统采用编/解码专用集成电路和单片机芯片来进行控制操作。设计的电路由如下的几个基本模块组成：直流稳压电源，红外发射电路，红外接收电路及控制部分。系统框图如图1所示。按键部分单片机89C2051发射部分电源3V图1 红外遥控电路框图 （a）发射电路框图5V接收部分单片机89C51显示部分控制部分电源9V图1 红外遥控电路框图 （b）接收电路框图（三）研究线路与关键技术红外遥控的特点是不影响周边环境的、不干扰其他电器设备。由于其无法穿透墙壁，故不同房间的家用电器可使用通用的遥控器而不会产生相互干扰；编解码容易，可进行多路遥控。 发射电路，利用遥控发射利用键盘，每按下一个键，即产生具有不同的编码数字脉冲，这种代码指令信号调制在40KHz的载波上，激励红外光二极管产生具有脉冲串的红外波，通过空间的传送到受控机的遥控接收器。 在接收过程中，红外波信号通过光学滤波器和光电二极管转换40KHZ的电信号，此信号经过放大，检波，整形，解调，送到解码与接口电路，从而完成相应的遥控功能。（四）、题的准备情况及进度计划；2006年10月15日2006年11月9 日第一周第二周第三周第四周第五周第六周第七周第八周下达毕业设计任务书开题报告查阅相关资料，确定设计方案；、设计电路设计电路方案确定提交中期报告、购买电子元器件焊接电路、软件编程、调试电路修改毕业论文、毕业论文预答辩撰写毕业论文、提交毕业论文初稿准备答辩，对设计内容进行总结，弄懂各部分的原理及系统的工作过程，写出毕业答辩的发言稿，做到心中有数，应对毕业答辩。参考文献：1 李振玉，姚光圻.高频放大及功率合成技术.北京:中国铁道出版社,1985年,第一版2 李锦春,蔡仁明.常用晶体二极管、大功率三极管手册.北京:人民邮电出版社,1981年,第一版3 康华光,邹寿彬.电子技术基础数字部分第四版.北京:高等教育出版社,2000年,第四版4 康华光,陈大钦.电子技术基础模拟部分第四版.北京:高等教育出版社,1999年,第四版5 杨振江,杜铁军,李群.流行单片机实用子程序与应用实例.西安:西安电子科技大学出版社,2002年,第一版6 铃木宪次.高频电路设计与制作.北京:科学出版社,2005年,第一版7 吴金戌,沈庆阳,郭庭吉.8051单片机实践与应用.北京:清华大学出版社,2002年,第一版8 李广弟,朱月秀,王秀山.单片机基础修订本.北京:北京航空航天大学出版社,2001年,第二版9 第二届全国大学生电子设计竞赛组委会.全国大学生电子设计竞赛获奖作品选编(1994-1995).北京:北京理工大学出版社,1997年,第一版10 全国大学生电子设计竞赛组委会.第四届全国大学生电子设计竞赛获奖作品选编(1999).北京:北京理工大学出版社,2001年,第一版11 全国大学生电子设计竞赛组委会.第五届全国大学生电子设计竞赛获奖作品选编(2001).北京:北京理工大学出版社,2003年,第一版12 全国大学生电子设计竞赛组委会.全国大学生电子设计竞赛获奖作品选编(2003).北京:北京理工大学出版社,2005年,第一版13 高吉祥.高频电子线路学习辅导及习题详解.北京:电子工业出版社,2005年,第一版14 谢自美.电子线路设计实验测试(第二版).武汉:华中科技大学出版社,2000年,第二版15 谭博学,苗汇静.集成电路原理以应用.北京:电子工业出版社,2003年,第一版16 黄智伟.全国大学生电子设计竞赛训练教程.北京:电子工业出版社,2005年,第一版17 刘征宇,韦立华.最新74系列IC特性代换手册.福建:福建科学技术出版社,2002年,第一版18 张俊谟.单片机中级教程(原理与应用).北京: 北京航空航天大学出版社,2000年,第一版19 张肃文.高频电子线路第四版.北京:高等教育出版社,2004年,第四版20 黄永定,唐克学.电子实验综合实训教程.北京:机械工业出版社,2004年,第一版4Tianjin University of Technology and Education毕 业 设 计专 业： 应用电子技术 班级学号： 应电041班 - 21 学生姓名： 陈春秀 指导教师： 葛颖 讲师 二七年 六 月天津工程师范学院专科生毕业设计(论文)红外遥控电路设计The design of circuit by infrared control 专业班级：应电041班学生姓名：陈春秀指导教师：葛颖 讲师系 别：电子工程系2007 年 6月摘 要随着科学技术的飞速发展，信息的飞快传播，红外遥控在人们的生活中已经成为不可或缺的部分。本文重点介绍了利用单片机AT89S52和AT89C2051实现红外发射和接收电路的设计方法。发射电路通过对单片机89C2051的编程，再通过红外二极管产生脉冲传送到接收器上。接收电路通过单片机AT89S52的控制编程，实现对不同设备的控制。整个电路耗电省、简单可靠、操作灵活、性能价格比高，较好地满足了现代生活，生产和科研的需要。关键词：红外遥控,发射电路,接收电路,单片机ABSTRACTWith the rapid development of technology, the rapid dissemination of information means that infrared control has become an indispensable component in peoples life. The article highlighted the design method of transmitting and receiving circuit by infrared control which use single-chip microcomputer AT89S52 and AT89C2051. After loading the program to the single-chip microcomputer 89C2051, by the transmitting circuit , the infrared diode turns out impulsion then transfer the single to the receiver. Receiving circuit use single-chip microcomputer AT89S52 which can program to control different equipments. The entire circuit is simple, reliable, flexible operation，high-performance, of high value and low cost, and it can meet the modern life, production and research need.Keywords： infrared control,transmitting circuit, receiving circuit,single-chip microcomputer目 录引言 11 设计要求及指标 22红外遥控系统的设计 33红外收发电路的设计4 3.1 主要芯片闪电存储型单片机AT89C51的介绍 4 3.2 89C2051 介绍 6 3.3 系统的功能实现方法7 3.4 红外发射电路 9 3.5 红外接收电路 9 3.6 软件设计 104直流稳压电源的设计14 4.1 直流稳压电源采用单相桥式整流电路14 4.2 滤波电路15 4.3 稳压电路165 LED显示电路的设计176控制部分197 调试结果及其分析218 结论22参考文献23附录1：发射程序24附录2：接收程序29附录3：红外发射接收电路总电路图33致谢34英文资料及中文翻译Radio Receiver A block diagram for a modern radio receiver is shown in Fig.2-4.The input signals to this radio are amplitude-modulated radio waves. The basic electronic circuits include: antenna ,tuner, mixer, local oscillator ,IF amplifier, audio detector, AF amplifier, loudspeaker, and power supply.Fig.2-4 A Block Diagram For Modern Radio ReceiverAny antenna system capable of radiating electrical energy is also able to abstract energy from a passing radio wave. Since every wave passing the receiving antenna. Induces its own voltage in the antenna conductor, it is necessary that the receiving equipment be capable of separating the desired signal from the unwanted signals that are also inducing voltages in the antenna. This separation is made on the basis of the difference in frequency between transmitting stations and is carried out by the use of resonant circuits, which can be made to discriminate very strongly in favor of a particular frequency. It has already been pointed that, by making antenna circuit resonant to a particular frequency, the energy abstracted from radio waves of that frequency will be much greater than the energy from waves of other frequencies; this alone gives a certain amount of separation between signals. Still greater selective action can be obtained by the use of additional suitably adjusted resonant circuits located somewhere in the receiver in such a way as to reject all but the desired signal. The ability to discriminate between radio waves of different frequencies is called selectivity and the process of adjusting circuits to resonance with the frequency of a desired signal is spoken of as tuning.Although intelligible radio signals have been received from the stations thousands of miles distant, using only the energy abstracted from the radio wave by the receiving antenna much more satisfactory reception can be obtained if the received energy is amplified. This amplification may be applied to the radio-frequency currents before detection, in which case it is called radio-frequency amplification or it may be applied to the rectified currents after detection, in which case it is called audio-frequency amplification. The use of amplification makes possible the satisfactory reception of signals from waves that would otherwise be too weak to give an audible response.The process by which the signal being transmitted is reproduced from the radio-frequency currents present at the receiver is called detection, or sometimes demodulation. Where the intelligence is transmitted by varying the amplitude of the radiated wave, detection is accomplished by rectifying the radio frequency current. The rectified current thus produced varies in accordance with the signal originally modulated on the wave irradiated at the transmitter and so reproduces the desired signal. Thus, when the modulated wave is rectified, the resulting current is seen to have an average value that varies in accordance with the amplitude of the original signal.Receiver circuit are made up a of a number of stages. A stage is a single transistor connected to components which provide operating voltages and currents and also signal voltages and currents. Each stage has its input circuit from which the signal comes in and its output circuit from which the signal, usually amplified, goes out. When one stage follows another, the output circuit of the first feeds the signal to the second. And so the signal is amplified, stage by stage, until it strong enough to operate the loudspeaker.Radio WavesRadio Waves are a member of the electromagnetic of waves. They are energy-carriers which travel at the speed of light (), their frequency() and wavelength() being related , as for any wave motion, by the equation =* where =c=3.0*108 m/s in a vacuum (or air). If =300m, then =/=3.0*108 /(3.0*10 2)=106Hz=1MHz. The smaller is, the larger . Radio Waves can be described either by their frequency or their wavelength. But the former is more fundamental since, unlike (and ), f does not change when the waves travel form one medium to another. Radio Waves can travel form a transmitting aerial in one or more of three different ways.Surface or ground wave. This travels along a ground, the curvature of the earths surface. Its range is limited mainly by the extent to which energy is absorbed form it by the ground. Poor conductors such as sand absorb more strongly that water, and the higher the frequency the greater the absorption. The range may be about 1500km at low frequencies (long wave, but much less for v. h. f.).Sky wave. This travels skywards and, if it is below a certain critical frequency (typically 30MHz), is returned to earth by the ionosphere. This consists of layers of air molecules (the D,E and F layer), stretching form about 80km above the earth to 50km, which have become positively charged through the removal of electrons by the suns ultraviolet radiation. On striking the earth the sky wave bounces back to the ionosphere where it is again gradually refracted and returned earthwards as if by reflection . This continues until it is completely attenuated.Space wave. For v. h . f., u. h. f. and microwave signals, only the space wave, giving line-of sight transmission, is effective. A range of up to 150km is possible on earth if the transmitting aerial is on high ground and there are no intervening obstacles such as hills, buildings or trees. OscillatorsElectrical oscillators are widely used in radio and television transmitters and receivers, in signal generators, oscilloscopes and computers, to produce A.C. with waveforms which may be sinusoidal, square, sawtooth etc. and with frequencies from a few hertz up to millions of hertz. Oscillatory circuit When a capacitor discharges through an inductor in a circuit of low resistance, an A.C. flows. The circuit is said to oscillate at its natural frequency which, as we will show shortly, equals, i.e. its resonant frequency f0. Electrical resonance thus occurs when the applied frequency equals the natural frequency as it does in a mechanical system.In Fig,2-2(a) , a charged capacitor C is shown connected across a coil L.C immediately starts to discharge, current flows and a magnetic field is created which induces an e. m. f. in L. This e. m. f. opposes the current . When C is completely discharged the electrical energy originally stored in the electric field between its plates has been transferred to the magnetic field around L. By the time the magnetic field has collapsed, the energy is again stored in C. Once more C starts to discharge but current now flows in the opposite direction, creating a magnetic field of opposite polarity. When this field has decayed, C is again charged with its upper plate positive and the same cycle is repeated. In the absence of resistance in any part of the circuit , an undamped sinusoidal A.C. would be obtained. In practice , energy is gradually dissipated by resistance as heat and a damped oscillation is produced.OscillatorAs the resistance of an LC circuit increases, the oscillation decay more quickly. To obtain undamped oscillations, energy has to be fed into the LC circuit in phase with its natural oscillations to compensate for the energy dissipated in the resistance of the circuit. This can be done with the help of a transistor in actual oscillators. A simple tuned oscillator is shown in Fig.2-2(b). The LC circuit is connected in the collector circuit (as the load) and oscillations start in it when the supply is switched on . The frequency of the oscillations is given by, i.e. then natural frequency of the LC circuit. The transistor merely ensures that energy is fed back at the correct instant from the battery. The current bias for the base of the transistor is obtained through R .AMPLIFIERIntroductionThe term amplifier is very generic. In general, the purpose of an amplifier is to take an input signal and make it stronger (or in more technically correct terms, increase its amplitude). Amplifiers find application in all kinds of electronic devices designed to perform any number of functions. There are many different types of amplifiers, each with a specific purpose in mind. For example, a radio transmitter uses an RF Amplifier (RF stands for Radio Frequency); such an amplifier is designed to amplify a signal so that it may drive an antenna. This article will focus on audio power amplifiers. Audio power amplifiers are those amplifiers which are designed to drive loudspeakers. Specifically, this discussion will focus on audio power amplifiers intended for DJ and sound reinforcement use. Much of the material presented also applies to amplifiers intended for home stereo system use.The purpose of a power amplifier, in very simple terms, is to take a signal from a source device (in a DJ system the signal typically comes from a preamplifier or signal processor) and make it suitable for driving a loudspeaker. Ideally, the ONLY thing different between the input signal and the output signal is the strength of the signal. In mathematical terms, if the input signal is denoted as S, the output of a perfect amplifier is X*S, where X is a constant (a fixed number). The * symbol means? Multiplied by. This being the real world, no amplifier does exactly the ideal, but many do a very good job if they are operated within their advertised power ratings. The output of all amplifiers contain additional signal components that are not present in the input signal; these additional (and unwanted)characteristics may be lumped together and are generally known as distortion. There are many types of distortion; however the two most common types are known as harmonic distortion and inter modulation distortion. In addition to the garbage traditionally known as distortion, all amplifiers generate a certain amount of noise (this can be heard as a background hiss when no music is playing). More on these later.All power amplifiers have a power rating, the units of power are called watts. The power rating of an amplifier may be stated for various load impedances; the units for load impedance are ohms. The most common load impedances are 8 ohms, 4 ohms, and 2 ohms (if you have an old vacuum tube amplifier the load impedances are more likely to be32 ohms, 16 ohms, 8 ohms, and maybe 4 ohms). The power output of a modern amplifier is usually higher when lower impedance loads (speakers) are used (but as we shall see later this is not necessarily better).In the early days, power amplifiers used devices called vacuum tubes (referred to simply as tubes from here on). Tubes are seldom used in amplifiers intended for DJ use (however tube amplifiers have a loyal following with musicians and hi-fi enthusiasts). Modern amplifiers almost always use transistors (instead of tubes); in the late 60s and early 70s, the term solid state was used (and often engraved on the front panel as a buzz word). The signal path in a tube amplifier undergoes similar processing as the signal in a transistor amp, however the devices and voltages are quite different. Tubes are generally high voltage low current devices, where transistors are the opposite (low voltage high current). Tube amplifiers are generally not very efficient and tend to generate a lot of heat. One of the biggest differences between a tube amplifier and a transistor amplifier is that an audio output transformer is almost always required in a tube amplifier (this is because the output impedance of a tube circuit is far too high to properly interface directly to a loudspeaker). High quality audio output transformers are difficult to design, and tend to be large, heavy, and expensive. Transistor amplifiers have numerous practical advantages as compared with tube amplifiers: they tend to be more efficient, smaller, more rugged (physically), no audio output transformer is required, and transistors do not require periodic replacement (unless you continually abuse them). Contrary to what many people believe, a well designed tube amplifier can have excellent sound (many high end hi-fi enthusiasts swear by them). Some people claim that tube amplifiers have their own particular sound. This sound is a result of the way tubes behave when approaching their output limits (clipping). A few big advantages that tube amplifiers have were necessarily given up when amplifiers went to transistors. What are Amplifier Classes?The Class of an amplifier refers to the design of the circuitry within the amp. There are many classes used for audio amps. The following is brief description of some of the more common amplifier classes you may have heard of. Class A: Class A amplifiers have very low distortion (lowest distortion occurs when the volume is low) however they are very inefficient and are rarely used for high power designs. The distortion is low because the transistors in the amp are biased such that they are half on when the amp is idling. As a result, a lot of power is dissipated even when the amp has no music playing! Class A amps are often used for signal level circuits (where power is small) because they maintain low distortion. Distortion for class A amps increases as the signal approaches clipping, as the signal is reaching the limits of voltage swing for the circuit. Also, some class A amps have speakers connected via capacitive coupling. Class B: Class B amplifiers are used in low cost, low quality designs. Class B amplifiers are a lot more efficient than class A amps, however they suffer from bad distortion when the signal level is low (the distortion is called crossover distortion). Class B is used most often where economy of design is needed. Before the advent of IC amplifiers, class B amplifiers were common in clock radio circuits, pocket transistor radios, or other applications where quality of sound is not that critical. Class AB: Class AB is probably the most common amplifier class for home stereo and similar amplifiers. Class AB amps combine the good points of class A and B amps. They have the good efficiency of class B amps and distortion that is a lot closer to a class A amp. With such amplifiers, distortion is worst when the signal is low, and lowest when the signal is just reaching the point of clipping. Class AB amps (like class B) use pairs of transistors, both of them being biased slightly ON so that the crossover distortion (associated with Class B amps) is largely eliminated. Class C: Class C amps are never used for audio circuits. They are commonly used in RF circuits. Class C amplifiers operate the output transistor in a state that results in tremendous distortion (it would be totally unsuitable for audio reproduction). However, the RF circuits where Class C amps are used employ filtering so that the final signal is completely acceptable. Class C amps are quite efficient. Class D: The concept of a Class D amp has been around for a long time, however only fairly recently have they become commonly used. Due to improvements in the speed, power capacity and efficiency of modern semiconductor devices, applications using Class D amps have become affordable for the common person. Class D amplifiers use a very high frequency signal to modulate the incoming audio signal. Such amps are commonly used in car audio subwoofer amplifiers. Class D amplifiers have very good efficiency. Due to the high frequencies that are present in the audio signal, Class D amps used for car stereo applications are often limited to subwoofer frequencies, however designs are improving all the time. It will not be too long before a full band class D amp becomes commonplace. Other classes: There are many other classes of amplifiers, such as G, H, S, etc. Most of these are variations of the class AB design, however they result in higher efficiency for designs that require very high output levels (500W and up for example). At this time I will not go into the details of all of these other classes as I have not studied them all in detail. Suffice to be aware that they exist for now. 无线电接收机图2-4为无线电接收机的方框图,输入信号为调幅无线电波。它的基本组成包括天线、调谐回路、混频器、本振电路、中放放大器、检波器、音频放大器、喇叭、电源等。任何天线系统既能辐射无线电波又能接收无线电波。任何经过天线的无线电波均能在天线中感应电压，因此，接收机必须能够从天线所收到的所有信号中分离出有用信号。这个分离过程是根据发射端发射的信号频率不同，利用调谐回路完成的。调谐回路能够有效地从众多频率中选择出某一个特定频率。通过天线调谐回路对某一特定频率地谐振，可以使天线从这一特定频率中吸收的能量比从其他平频率中吸收的能量大得多，这样，就从某种程度上实现了信号的分离。进一步的选择作用可以通过接收机中的某些经过适当调谐的谐振回路实现，以这种方式进一步去除了有用信号以外的其他信号。将不同频率的无线电波加以区别的能力称为选频，将谐振回路的频率调在有用信号频率上的过程称为调谐。尽管接收的有用信号来自几千里以外，但如果经过放大，通过天线获得的信号还是具有令人满意的效果。放大过程可能应用在对检波前的射频电流，这种情况称为射频放大；也可应于检波后，这种情况称为音频放大。放大器的应用使令人满意的接收成为可能，否则，有些太弱的信号不能获得好的收听效果。从射频信号中重视被传输的原始信号的过程称为检波或解调。如果有用信号在发射时是通过改变信号的振幅（即调幅），则检波就是通过对射频电流进行整流完成的。整流电流随着原始调制信号而变化，从而冲县了原始的有用信号，这样，已调波被整流而产生的电流可以被看成随原始信号幅度变化的平均值电流。接收机的电路由多级组成。每级由晶体管与提供工作电压、电流和信号电压、电流的元件相连构成，每级都有输入回路，它让信号进入；有输出回路，它让通常是放大后的信号输出。当一级接一级时，第一级的输出回路将信号馈送给第二级，信号经过逐级放大，直到足以推动扬声器。无线电波无线电波是电磁波大家族中的一员，它们携带能量且以光速在空气中传播，它们的频率与波长相关，即任何电磁波传播时，有 =* 这里，=c=3.0*108 m/s（在空气中），如果=300m,则=/=3.0*108 /(3.0*10 2)=106Hz.=1MHz。波长越小，频率越高。无线电波既能用频率又能用波长来描述。但前者更常用，因为频率不像速度，不会因传播媒介的改变而变化。从天线电波辐射出去的无线电波通常以三种形式传播。（a）地表波或地波。这种波按地球表面的曲度，沿地表面传播。它的传播范围有限，其能量易被地表面吸收。恶劣的地形条件如沙漠比水面更易吸收能量。频率越高，能量被吸收得越多。低频波（长波）的传播范围约为1500千米。高频波的查范围要小得多。（b）天波。沿天空传播，若低于某个关键频率（如30MHZ），会被电离层反射回地面。电离层由空气分子层组成（包括D、E、F层），位于地球上方